The imported fire ants (IFA), Solenopsis invicta and Solenopsis richteri were introduced into the United States in the early 1900's at the port of Mobile, Ala. By the late 1940's and early 1950's these fire ants, particularly S. invicta, were present at nurseries from Miami, Fla. to San Antonio, Tex. and as far north as North Carolina. Imported fire ants displace the native ant fauna and, in many areas of the southeastern United States, have become the dominant ant species. IFA have colonized a wide range of habitats and have proven to be particularly successful at colonizing disturbed lands such as cultivated farmland. Currently, the imported fire ants infest 230 million acres in the southern United States, including all 67 counties in Florida. Solenopsis invicta is the species responsible for over 95% of the infestation in the United States.
The imported fire ant has gained notoriety primarily as a result of its painful sting and its inclination to feed on a wide array of materials, including cultivated plants and underground wires. The fire ant sting is not only painful but is potentially life threatening for people who suffer from an allergic reaction to the sting.
Fire ants live in nests in the ground, therefore, they are a particular nuisance in schoolyards, recreational areas, and homeowners' yards. Although the nests are often underground, they may reach 1 to 2 feet in height above the ground. These mounds are especially troublesome for homeowners because they present a hazard for children and pets, in addition to being unsightly.
Farmers throughout the southern states have suffered large economical losses as the result of fire ant infestations. Fire ants reduce the active foraging area in pastures because animals do not forage well around fire ant nests. Fire ants may also damage plants by chewing on stems or fruits. IFA has been reported to cause serious damage in young citrus groves and in vegetable crops with high cash values. Also, these ants make it difficult to harvest some crops such as hay and citrus. Large fire ant mounds may also cause damage to agricultural equipment especially in heavy clay soil areas.
Additional economic loss has resulted from the IFA chewing on electrical wiring and telephone lines in the ground or even housed in containers above the ground.
In response to the then serious economic and public safety threat, well over $200 million was spent by the state and federal governments between 1950 and 1982 in efforts to control or eradicate these ants. Additional funds have also been provided by local agencies, as well as private citizens. Despite this tremendous commitment of resources in an attempt to control these pests, IFA have spread, largely unchecked, through the southeastern United States.
Control efforts to date have focused on the identification of chemical control agents. Unfortunately, the use of chemical control agents has been largely ineffective and can, in fact, lead to increased populations of IFA. This increase occurs in the following way: broadcast application of non-specific formicides results in the temporary control of all ant species; then, IFA reinfests the area faster than native ant species. The net result is an inadvertent increase in IFA populations, allowing IFA to become the dominant species more quickly than if no control action were taken. IFA nest densities can increase more than 30-fold within 1 to 2 years following broadcast chemical treatment of an area where IFA densities are initially low.
In addition to being ineffective in the battle to control IFA, chemical control agents present the usual hazards associated with the use of chemical pesticides. These hazards include the poisoning of soil and underlying aquifiers; pollution of surface waters as a result of runoff; and the destruction of non-target life forms.
Chemical control agents have the further disadvantage of presenting public safety hazards when they are applied in areas where pets, farm animals, or children may come in contact with them. This makes chemical agents particularly disadvantageous for the control of IFA in school yards, pasture lands, and residential areas.
Because of the ineffectiveness of chemical control agents, as well as, the many health and environmental problems associated with their use, increasing research attention has turned toward the development of biological control agents. Unfortunately the search for biological control agents has been largely unfruitful. No predators, parasites, or pathogens indigenous to the United States have proven to be effective biological controls of IFA, although some native ant species may retard IFA colonization in areas that are not frequently or severely disturbed.